1. Field of the Invention
The invention relates to a motor driving apparatus, and more particularly to circuit elements in a semiconductor integrated circuit such as motor driving LSI for driving a motor when the motor is going out of speed controllable range due to abnormal excessive load by external factors, or to a protection technology for preventing winding coils of a motor from being broken down.
2. Related Art
Conventional control method of a brushless motor detects a rotating speed of a rotor using a detecting element such as a Hall element. A speed control circuit compares the detected speed information with a target speed signal to generate a speed control signal for controlling the rotating speed of the motor.
When a brushless motor rotating at a constant speed is stopped by force due to external load applied to the rotor of the motor, a rotating speed signal is not applied to the speed control motor because the motor is stopped. As a result, the speed control circuit judges that the motor does not reach the target rotating speed, and continues to issue a speed control signal to instruct a full acceleration. Consequently, a large current continues to flow in output transistors for driving the motor, possibly leading to breakdown of output transistors or breakdown of winding coils of the brushless motor.
To avoid such problems, a technology is disclosed, for example, in patent document 1. Patent document 1 discloses a protective technology in the event of forced stop of rotor due to external load applied to rotor or other parts of brushless motor during rotation at constant speed.
Patent document 1: JP-A-5-122834
The protection technology in the conventional motor driving apparatus disclosed in patent document 1 is designed to operate a protection circuit after complete stop of the motor and complete stop of output of the motor position detection signal (or rotating speed signal). Hence, when much time elapses until the motor stops completely due to abnormal excessive load caused by certain external factors, it takes much time to start the protecting operation. As a result, a duration for which a large current flows in the output transistor for driving the motor is increased, and the output transistor may be broken or a stator winding of the brushless motor may be broken.
In the event of abnormal excessive load by certain external factor not stopping the motor completely, the motor position detection signal continues to be issued, and the protecting operation does not function. As a result, a large current continues to flow in the output transistor for driving the motor, resulting in breakdown of the output transistor or the stator windings of the brushless motor.